Mosquitoes are important vectors for a number of infectious diseases caused by arboviruses including West Nile virus, dengue virus, yellow fever virus, LaCrosse virus, and Venezuelan, eastern and western equine encephalitis viruses. Mosquitoes acquire arboviruses from vertebrate hosts during blood feeding, and after entry into the mosquito vector, the virus must first infect, replicate in, and escape from the epithelial cells of the midgut before it can be disseminated to other organs. Dissemination to the salivary glands is necessary for transmission to another host. Thus, the midgut epithelium constitutes a potential barrier to infection and subsequent transmission, and is therefore a target for interrupting the transmission cycle. It is well documented that only certain vector-virus combinations result in efficient transmission of disease, and data exist indicating that arboviruses must overcome the immune defenses of the insect vector in order to be transmitted successfully. However, little is known about anti-viral defenses in insects. For several years the Clem laboratory has been studying the role of apoptosis in defense against baculovirus infection in lepidopteran insects. This application seeks to explore the question of whether apoptosis can serve as a defense against arbovirus invasion in the mosquito midgut. In order to accomplish this goal a strong and diverse team has been assembled that includes expertise in apoptosis, mosquito vector biology, and arboviruses. In Aim 1, midguts and other tissues from arbovirus-infected mosquitoes will be examined for apoptosis, including a collection of Aedes aegypti strains that vary in their ability to vector dengue virus. In Aim 2, the hypothesis that apoptosis can limit virus replication and spread will be directly tested by manipulating apoptotic pathways in the mosquito and examining the effects on the ability of arboviruses to successfully cause disseminated infections. [unreadable] [unreadable]